The voice of the new imam at one of the largest mosques on the East Coast rang loud from the pulpit during Friday services: "The call to reform Islam is an alien call."

People who do not understand Islam are the ones seeking to change it, said Shaker Elsayed, the new spiritual leader at the Dar al-Hijrah mosque in Falls Church.

"Ignorance comes from outside circles who know nothing about us," Mr. Elsayed said during noon services to more than 500 men and women, with women worshipping in a separate room. It was one of three services Dar al-Hijrah holds every Friday.

Mr. Elsayed, who assumed duties as imam of the mosque June 1, is well known in the Muslim community for his political activism.

He has served as secretary general of the Muslim American Society, an advocacy group that some accuse of promoting a fundamentalist strain of Islam.

He also has served as an unofficial spokesman for the family of Ahmed Omar Abu Ali, who is accused of joining al Qaeda while studying overseas and plotting to assassinate President Bush. Mr. Abu Ali grew up in Falls Church and worshipped at Dar al-Hijrah.

Mr. Elsayed has accused the Justice Department of unfairly targeting Mr. Abu Ali and other young Muslims for prosecution.

Perhaps not surprisingly then, Mr. Elsayed's sermons take a political tone.

"Islam forbids you to give allegiance to those who kick you off your homeland, and to those who support those who kick you off your homeland," he told worshippers. "We do have license to respond with all force necessary to answer our attackers."

Mr. Elsayed explained after the sermon that opposition to U.S. policy in the Middle East is different than viewing the American people as the enemy.

Asked his views on militant groups such as Hamas, which the U.S. government has designated as a terrorist organization, Mr. Elsayed compared Hamas to Nelson Mandela's African National Congress -- organizations that resorted to violent resistance only after decades of injustice.

"Everybody jumps on Hamas," Mr. Elsayed said. "When did Hamas first emerge? 1990 or so? Look at how long Israel has occupied [Palestinian lands]. How long did it take to say enough is enough?"

Still, he said support for Hamas' objectives does not mean he always supports the group's tactics, which have included suicide bombings.